The present invention concerns an anchoring device and a process for the placement of grout anchors having the purpose of securing the stability of a structure relative to ground, and involving the drilling of a hole to an anchoring zone in the ground, the introduction of cables and/or other anchoring reinforcements into the drilled hole, and the injection of a cement slurry through said drilled hole so as to form a grout body in said anchoring zone.
Conventional processes of this type require several cement injections for formation of the grout body, for example injections with sleeves which must be separated in time, thus usually requiring several days for formation of the grout body. Moreover, the load bearing strength remains limited, particularly in clayey and loamy grounds, notably because of the limited transverse dimensions of the grout body that can be achieved by the known processes and because of the poor control of formation of this body and its composition, which essentially remains injected cement.
The document EP-A-0 413 676 describes a process of the above mentioned type in which a tool is used that comprises a drilling tool portion and exhibits an axial channel which is the extension of an injection channel, while a valve is so arranged at the entrance of said axial channel that the said entrance can be closed off prior to injection of a cement slurry under pressure through the central channel and said axial channel.
The document EP 0 770 734 describes a process in which the drilling is performed by means of a pipe which, at its front end, is fitted with a drilling and injection tool, this pipe forming a cement injection channel and said tool comprising at least two lateral nozzles pointing in opposite directions. The nozzles are part of a drilling tool having an axial channel which is an extension of said injection channel, while a valve is so arranged between the entrance of said axial channel and said nozzles that said entrance can be closed off prior to injection of the cement slurry under pressure. The cement slurry is injected with a pressure higher than about 40 MPa (400 bar) into the surrounding ground through said nozzles in a direction radial to said pipe while the pipe is turned about its own axis and pulled back in a continuous or discontinuous fashion over a certain bond length. The injection is then stopped and the pipe fully withdrawn. Prior to hardening of the cement, said cables and/or other anchoring reinforcements are introduced into the drilled hole and grout body being formed.
An object of this invention is to provide an improved anchoring device and an improved process for the placement of grout anchors, in particular a device and respective process of the above-mentioned type where the anchorage is further improved and the operation of placement of the grout anchors simplified and accelerated.
Objects of the invention are achieved by a process comprising the step of drilling a hole by means of a column drill comprising a drilling pipe having at its front end an injection tool and a drilling tool coupled to the injection tool, this pipe forming a cement injection channel and said injection tool comprising at least one or several nozzles allowing a cement slurry to be injected under pressure into the surrounding ground in order to form a grout body, said drilling tool being attached to one or several anchor cables or other anchoring reinforcements, wherein the process further comprises the steps of injecting cement slurry into the surrounding ground and around the anchoring reinforcements and drilling tool, and withdrawing the pipe while leaving the drilling tool in the grout body.
The drilling and anchoring device comprises a column with a drilling pipe, a drilling tool mounted at the pipe""s end, and one or several cables and/or other anchoring reinforcements, wherein the cables and/or other anchoring reinforcements are so attached to the drilling tool that the drilling tool remains in a grout body formed by cement injection in the ground surrounding a drilling hole.
The injection tool is preferably equipped with two lateral nozzles pointing in opposite directions and at least one terminal nozzle pointing obliquely toward the central axis of the pipe within which run the cables and/or other anchoring reinforcements. The drilling tool comprises a coupling parties which axially separably slips into the axial channel of the pipe.
During the drilling operation, water under pressure is brought through an axial channel to the drilling tool. The axial channel may be constituted by an inner pipe coaxial with the drilling pipe. The inner pipe may be equipped with a valve, in its upper part for instance, in order to control the supply of water under pressure to the drilling tool during the drilling operation and during the operation of withdrawing the column drill after formation of the grout body.
The space between the drilling pipe and the inner pipe may constitute the cement injection channel.
The terminal nozzle subtends an acute angle to the axial direction, of 30xc2x0 for instance, so that the cement slurry jet issuing from this nozzle applies a force component in the axial direction to the drilling tool. This allows the drilling tool to be separated from the drilling pipe during formation of the grout body. This nozzle also ensures that the cables and/or other anchoring reinforcements be fully immersed into the grout body.
The device and process according to the invention thus provide a very good anchoring with very few operations and great speed.
The invention also prevents problems from arising when anchoring reinforcements are reintroduced into the drilling hole in conventional processes.
Moreover, the density of reinforcements placed into the axial channel of the pipe can be optimized when the anchoring reinforcements are attached to the drilling tool and are inserted in advance into the drilling pipe, that is, prior to the drilling operation.
Attaching the drilling tool to the end of the anchoring reinforcements also improves the retention of these reinforcements in the grout body.
Features, objectives and advantages of the process according to the invention will appear more clearly from the following description provided as an example and illustrated in the appended drawings.